1. Field of the Invention
This invention refers to a system for indicating economy of operation in internal combustion engines in boats so as to make it feasible to set a specific number of revolutions of the engines for achieving fuel economy.
2. Description of the Prior Art
In the operation of boats or other craft having internal combustion engines the power requirements and thus the consumption of fuel often increase heavily with the speed or number of revolutions of the engine of the boat. In boats the consumed power may be expressed as the product of a braking force on the hull and the speed. The braking force is caused on one hand by the friction against the water, which increases approximately with the square of the speed, and on the other hand by the resistance of the shape and waves, with the latter resistance being affected by the relationship of the length of the hull and the length of the generated waves at the relevant speed. Furthermore, the braking force is influenced as the result of the wet area of the boat varying with the speed. The requirement of power may be expressed as a sum of exponential terms with the exponents varying between 1 and 4 and an additional interference term which changes between a positive and a negative value at different speeds. In conditions of operation in which the interference term is positive the power consumption becomes greater than the "average value" adjusted to the relevant speed.